One of the significant problems with heat pumps is that occasionally the reversing valve may fail to change from heating to cooling, or from cooling to heating, when commanded by the system controls. Accordingly, the heat pump may be providing cooling to the controlled space, e.g., building, when heating of same is required or be providing heating when cooling is required; this type of malfunction may waste energy and may damage the heat pump system. Accordingly, prior art technology identifies the relationship between the heating or cooling mode of operation of the heat pump and the difference between the outdoor heat exchanger coil refrigerant temperature and the outdoor air temperature, and various prior art schemes protect the heat pump from potentially damaging excessive pressures resulting from, for example, attempting to provide cooling for the controlled space when the outdoor temperature is cooler than would be normal for cooling operation; however, all of these prior art arrangements have shortcomings in that they fail to respond to this type of failure of the heat pump system until damage to the heat pump system components is imminent, without attending to the problem of wasting energy.
For example, one prior art scheme monitors the pressure of the refrigerant at the discharge side of the compressor and inhibits the compressor operation when said pressure exceeds a predetermined value; this scheme protects the heat pump system from damage due to this fault, but does not respond to this fault unless the temperatures of the indoor and outdoor heat exchangers are high enough to cause an extreme rise in said discharge refrigerant pressure, and furthermore, this scheme does not protect against wasted energy resulting when this fault occurs under circumstances which do not produce excessive discharge refrigerant pressures.
An object of the present invention is to provide a new and significantly improved means of responding to the conditions of a reverse cycle refrigeration system is heating when it should be cooling or cooling when it should be heating.